/*
 * Copyright 2014-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.data.keyvalue.core;

import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.List;
import java.util.UUID;
import java.util.concurrent.atomic.AtomicReference;

import org.springframework.dao.InvalidDataAccessApiUsageException;
import org.springframework.data.util.TypeInformation;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

/**
 * Default implementation of {@link IdentifierGenerator} to generate identifiers of types {@link UUID}, String,
 *
 * @author Christoph Strobl
 * @author Oliver Gierke
 */
enum DefaultIdentifierGenerator implements IdentifierGenerator {

	INSTANCE;

	private final AtomicReference<SecureRandom> secureRandom = new AtomicReference<>(null);

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.keyvalue.core.IdentifierGenerator#newIdForType(org.springframework.data.util.TypeInformation)
	 */
	@Override
	@SuppressWarnings("unchecked")
	public <T> T generateIdentifierOfType(TypeInformation<T> identifierType) {

		Class<?> type = identifierType.getType();

		if (ClassUtils.isAssignable(UUID.class, type)) {
			return (T) UUID.randomUUID();
		} else if (ClassUtils.isAssignable(String.class, type)) {
			return (T) UUID.randomUUID().toString();
		} else if (ClassUtils.isAssignable(Integer.class, type)) {
			return (T) Integer.valueOf(getSecureRandom().nextInt());
		} else if (ClassUtils.isAssignable(Long.class, type)) {
			return (T) Long.valueOf(getSecureRandom().nextLong());
		}

		throw new InvalidDataAccessApiUsageException("Non gereratable id type....");
	}

	private SecureRandom getSecureRandom() {

		SecureRandom secureRandom = this.secureRandom.get();
		if (secureRandom != null) {
			return secureRandom;
		}

		for (String algorithm : OsTools.secureRandomAlgorithmNames()) {
			try {
				secureRandom = SecureRandom.getInstance(algorithm);
			} catch (NoSuchAlgorithmException e) {
				// ignore and try next.
			}
		}

		if (secureRandom == null) {
			throw new InvalidDataAccessApiUsageException(
					String.format("Could not create SecureRandom instance for one of the algorithms '%s'.",
							StringUtils.collectionToCommaDelimitedString(OsTools.secureRandomAlgorithmNames())));
		}

		this.secureRandom.compareAndSet(null, secureRandom);

		return secureRandom;
	}

	/**
	 * @author Christoph Strobl
	 * @since 1.1.2
	 */
	private static class OsTools {

		private static final String OPERATING_SYSTEM_NAME = System.getProperty("os.name").toLowerCase();

		private static final List<String> SECURE_RANDOM_ALGORITHMS_LINUX_OSX_SOLARIS = Arrays.asList("NativePRNGBlocking",
				"NativePRNGNonBlocking", "NativePRNG", "SHA1PRNG");
		private static final List<String> SECURE_RANDOM_ALGORITHMS_WINDOWS = Arrays.asList("SHA1PRNG", "Windows-PRNG");

		static List<String> secureRandomAlgorithmNames() {
			return OPERATING_SYSTEM_NAME.contains("win") ? SECURE_RANDOM_ALGORITHMS_WINDOWS
					: SECURE_RANDOM_ALGORITHMS_LINUX_OSX_SOLARIS;
		}
	}
}
